A national Tea Party group is going on air next week in Kansas, attacking Sen. Pat RobertsCharles (Pat) Patrick RobertsThe Hill's Whip List: Republicans try again on ObamaCare repeal No. 2 Senate Republican backs McConnell in Trump fight Overnight Healthcare: McConnell warns Senate not to block repeal debate | Insurers knock Cruz proposal | WH tries to discredit CBO | Lawmakers propose .1B NIH funding boost MORE (R-Kan.) as he heads into the final week of his primary fight with radiologist Milton Wolf.

Tea Party Patriots Citizens Fund, which has endorsed Wolf, is investing about $75,000 in advertising in the state next week, a source close to the group tells The Hill. No further details on the buy were available, though the relatively small sum isn’t enough to saturate the airwaves in the state.

Roberts is heavily favored in his primary fight with Wolf, but his supporters remain wary of a possible last-minute influx of outside spending from conservative groups. 

However, many of the national conservative groups, including Citizens Fund, have little to spend coming out of a costly and expensive primary fight in Mississippi, which they lost.

And Wolf’s campaign suffered another setback this week, with the revelation that a state ethics board has launched an investigation into Facebook postings of his in which he gave off-color commentary on X-rays, which he’s claimed broke no rules and did not belong to his patients. 

The initial report outlining those posts stalled Wolf’s campaign earlier this year, and now the investigation has given the Roberts campaign further fodder for attacks. It launched a new television ad Friday highlighting the investigation and declaring Wolf “unfit, not trusted, not right for Kansas.”